Data collection and transfer apparatuses have been used that collect control data related to a control device and transfer the control data to the upper-level server, connected via a LAN, for the operating state of the control device and the state of the control target to be remotely monitored and analyzed. Such data collection and transfer apparatuses temporarily store data collected from the control device in a memory device (hereinafter, a temporary memory) capable of reading and writing at high speed and then transfers the data to the upper-level server at a given time.
The data collection and transfer apparatus collects data related to the control device and stores the data in the temporary memory, and then transfers the data to the upper-level server at a given time. However, when a fault occurs in the network between the data collection and transfer apparatus and the upper-level server, the data stored in the temporary memory cannot be transferred to the upper-level server. Moreover, when the memory capacity of the temporary memory is not sufficiently large, not all the data related to the control device collected while a network fault is occurring can be stored. In other words, there is a problem in that it is impossible to monitor and analyze the operating state of the control device and the state of the control target while a network fault is occurring.
In order to solve such a problem, the following data collection and transfer apparatus has been proposed. The apparatus is configured from a control device that performs a predetermined control and retains data related to this control and a data collection and transfer apparatus that has a function of, after collecting control data related to the control device and storing the control data in the temporary memory, transferring the data stored in the temporary memory to the upper-level server at a given time and a means (hereinafter, referred to as buffering) for, when a fault is detected in the network between the data collection and transfer apparatus and the upper-level server, storing, in order, the data stored in the temporary memory in a memory that can store large-capacity data (hereinafter, referred to as a large-capacity buffer memory).
A method for taking a measure against a fault in a measured data collection system is proposed in Patent Literature 1. This measured data collection system has a mode switching unit that switches the personal computer terminal in the personal computer, which is connected via a line to the host computer system, from the online mode to the local mode when a fault occurs and switches the personal computer terminal from the local mode to the online mode when the fault is rectified and a measured-data continuous collection and storage unit that continuously collects online-mode measured data and local-mode measured data before and after the occurrence of a fault and stores the data in an external storing device in the personal computer.